[...] fifty thousand years ago there were these three guys spread out across the plain, and they each heard something rustling in the grass. The first one thought it was a tiger, and he ran like hell, and it was a tiger but the guy got away. The second one thought the rustling was a tiger, and he ran like hell, but it was only the wind and his friends all laughed at him for being such a chickenshit. But the third guy, he thought it was only the wind, so he shrugged it off and a tiger had him for dinner. And the same thing happened a million times across ten thousand generations — and after a while everyone was seeing tigers in the grass even when there weren’t any tigers, because even chickenshits have more kids than corpses do. And from those humble beginnings we learned to see faces in the clouds and portents in the stars, to see agency in randomness, because natural selection favors the paranoid. Even here in the twenty-first century you can make people more honest just by scribbling a pair of eyes on the wall with a Sharpie. Even now, we are wired to believe that unseen things are watching us.
And it came to pass that certain people figured out how to use that. They painted their faces or they wore funny hats, they shook their rattles and waved their crosses and they said, Yes, there are tigers in the grass, there are faces in the sky, and they will be very angry if you do not obey their commandments. You must make offerings to appease them, you must bring grain and gold and altar boys for our delectation or they will strike you down and send you to the Awful Place. And people believed them by the billions, because after all, they could see the invisible tigers. Peter Watts - Echopraxia